Scalability of all-optical neural networks based on spatial light modulators

Author(s):

Ying Zuo, Zhao Yujun, You-Chiuan Chen, Shengwang Du & Liu, Junwei

Abstract:

“Optical implementation of artificial neural networks has been attracting great attention due to its potential in parallel computation at speed of light. Although all-optical deep neural networks (AODNNs) with a few neurons have been experimentally demonstrated with acceptable errors re- cently, the feasibility of large scale AODNNs remains unknown because error might accumulate inevitably with increasing number of neurons and connections. Here, we demonstrate a scalable AODNN with programmable linear operations and tunable nonlinear activation functions. We ver- ify its scalability by measuring and analyzing errors propagating from a single neuron to the entire network. The feasibility of AODNNs is further confirmed by recognizing handwritten digits and fashions respectively.”

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Publication: Physical Review Applied
Issue/Year: Physical Review Applied, 2021
DOI: https://doi.org/10.1103/PhysRevApplied.15.054034

Neural 3D holography

Author(s):

Choi, Suyeon; Gopakumar, Manu; Peng, Yifan; Kim, Jonghyun & Wetzstein, Gordon

Abstract:

“Holographic near-eye displays promise unprecedented capabilities for virtual and augmented reality (VR/AR) systems. The image quality achieved by current holographic displays, however, is limited by the wave propagation models used to simulate the physical optics. We propose a neural network-parameterized plane-to-multiplane wave propagation model that closes the gap between physics and simulation. Our model is automatically trained using camera feedback and it outperforms related techniques in 2D plane-to-plane settings by a large margin. Moreover, it is the first network-parameterized model to naturally extend to 3D settings, enabling high-quality 3D computer-generated holography using a novel phase regularization strategy of the complex-valued wave field. The efficacy of our approach is demonstrated through extensive experimental evaluation with both VR and optical see-through AR display prototypes.”

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Publication: ACM Transactions on Graphics
Issue/Year: ACM Transactions on Graphics, Volume 40; Number 6; Pages 1–12; 2021
DOI: 10.1145/3478513.3480542

Metamachines of pluripotent colloids

Author(s):

Aubret, Antoine; Martinet, Quentin & Palacci, Jeremie

Abstract:

“Machines enabled the Industrial Revolution and are central to modern technological progress: A machine’s parts transmit forces, motion, and energy to one another in a predetermined manner. Today’s engineering frontier, building artificial micromachines that emulate the biological machinery of living organisms, requires faithful assembly and energy consumption at the microscale. Here, we demonstrate the programmable assembly of active particles into autonomous metamachines using optical templates. Metamachines, or machines made of machines, are stable, mobile and autonomous architectures, whose dynamics stems from the geometry. We use the interplay between anisotropic force generation of the active colloids with the control of their orientation by local geometry. This allows autonomous reprogramming of active particles of the metamachines to achieve multiple functions. It permits the modular assembly of metamachines by fusion, reconfiguration of metamachines and, we anticipate, a shift in focus of self-assembly towards active matter and reprogrammable materials.”

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Publication: Nature Communications
Issue/Year: Nature Communications, Volume 12; Number 1; 2021
DOI: 10.1038/s41467-021-26699-6

Speckle-free holography with partially coherent light sources and camera-in-the-loop calibration

Author(s):

Peng, Yifan; Choi, Suyeon; Kim, Jonghyun & Wetzstein, Gordon

Abstract:

“Computer-generated holography (CGH) holds transformative potential for a wide range of applications, including direct-view, virtual and augmented reality, and automotive display systems. While research on holographic displays has recently made impressive progress, image quality and eye safety of holographic displays are fundamentally limited by the speckle introduced by coherent light sources. Here, we develop an approach to CGH using partially coherent sources. For this purpose, we devise a wave propagation model for partially coherent light that is demonstrated in conjunction with a camera-in-the-loop calibration strategy. We evaluate this algorithm using light-emitting diodes (LEDs) and superluminescent LEDs (SLEDs) and demonstrate improved speckle characteristics of the resulting holograms compared with coherent lasers. SLEDs in particular are demonstrated to be promising light sources for holographic display applications, because of their potential to generate sharp and high-contrast two-dimensional (2D) and 3D images that are bright, eye safe, and almost free of speckle.”

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Publication: Science Advances
Issue/Year: Science Advances, Volume 7; Number 46; 2021
DOI: 10.1126/sciadv.abg5040

Realization and measurement of Airy transform of Gaussian vortex beams

Author(s):

Zhou, Lu; Zhou, Tong; Wang, Fei; Li, Xia; Chen, Ruipin; Zhou, Yimin & Zhou, Guoquan

Abstract:

“Airy transformation is a useful technique to modulate amplitude and phase of a light beam, which has important applications in particle trapping/manipulation, optical communications and optical imaging. However, most of the studies only focused on the Airy transform of Gaussian beams and other vortex-free beams in the past. In this paper, the Airy transform of Gaussian vortex beams, which are the most common vortex beams, is investigated. A universal analytical expression of the Gaussian vortex beams with topological charge (TC) m passing through an Airy transform optical system is derived. We carry out a detailed study on the output beams’ characteristics after the Airy transform of the Gaussian vortex beams with m = ± 1 and ± 2. The analytical expressions for the centroid, the beam spot size, the divergence angle and the beam propagation factor of the output beams are derived. The effects of the Airy control parameters and the TC on the normalized intensity distribution, the phase distribution, the centroid, the beam spot size and the beam propagation factor of the output beams are investigated both theoretically and experimentally. The experimental results agree reasonably well with the theoretical results which illustrate the properties of Airy transform of the Gaussian vortex beams.”

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Publication: Optics and Laser Technology
Issue/Year: Optics and Laser Technology, Volume 143; Pages 107334; 2021
DOI: 10.1016/j.optlastec.2021.107334

Unfiltered holography: optimizing high diffraction orders without optical filtering for compact holographic displays

Author(s):

Gopakumar, Manu; Kim, Jonghyun; Choi, Suyeon; Peng, Yifan & Wetzstein, Gordon

Abstract:

“Computer-generated holography suffers from high diffraction orders (HDOs) created from pixelated spatial light modulators, which must be optically filtered using bulky optics. Here, we develop an algorithmic framework for optimizing HDOs without optical filtering to enable compact holographic displays. We devise a wave propagation model of HDOs and use it to optimize phase patterns, which allows HDOs to contribute to forming the image instead of creating artifacts. The proposed method significantly outperforms previous algorithms in an unfiltered holographic display prototype.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Volume 46; Number 23; Pages 5822; 2021
DOI: 10.1364/ol.442851

Experimental investigation in Airy transform of Gaussian beams with optical vortex

Author(s):

Xu, Yi-Qing; Li, Xia; Zhou, Lu; Zhou, Yi-Min; Wang, Fei & Zhou, Guo-Quan

Abstract:

“The Airy transform was first introduced for a Gaussian beam, and the output beam is an Airy beam. When the Gaussian beam is extended to the Gaussian beam with optical vortex, what kind of output beam will be achieved by executing the Airy transformation. Therefore, the experimental research on Airy transformation of a Gaussian beam with optical vortex is carried out, including the generation of Gaussian beams with optical vortex, the realization of Airy transform, and the related measurements of the output beams. The phase pattern is indirect measured and is recovered from the intensity pattern which is the interference result of a plane wave and the output beam. The experimental measurement results of the light intensity and the phase patterns of transformed Gaussian beams with the optical vortex are consistent with the corresponding numerical simulation results.

Based on the first and the second moments of light intensity, the centroid and the beam size are measured. According to the hyperbolic law of the beam width along the axial propagation distance, the propagation factor of the output beam is measured. The influences of the Airy coefficients and the topological charge on the intensity pattern, the phase pattern, the centroid, the beam size, and the propagation factor of transformed Gaussian beams with optical vortex are experimentally investigated, respectively. The intensity pattern, the phase pattern, the centroid, the beam size, and the propagation factor of a transformed Gaussian beam with optical vortex are also compared with those of the corresponding transformed Gaussian vortex beam. This experiment fully proves the effect of the optical vortex on the Airy transformation of Gaussian beams. Meanwhile, this study offers an optional method to generate Airy-like beams from Gaussian beams with optical vortex, which is beneficial to the applications of Gaussian beams with optical vortex.”

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Publication: Results in Physics
Issue/Year: Results in Physics, Volume 28; Pages 104588; 2021
DOI: 10.1016/j.rinp.2021.104588

DL-SI-DHM: a deep network generating the high-resolution phase and amplitude images from wide-field images

Author(s):

Meng, Zhang; Pedrini, Giancarlo; Lv, Xiaoxu; Ma, Jun; Nie, Shouping & Yuan, Caojin

Abstract:

“Structured illumination digital holographic microscopy (SI-DHM) is a high-resolution, label-free technique enabling us to image unstained biological samples. SI-DHM has high re- quirements on the stability of the experimental setup and needs long exposure time. Furthermore, image synthesizing and phase correcting in the reconstruction process are both challenging tasks. We propose a deep-learning-based method called DL-SI-DHM to improve the recording, the reconstruction efficiency and the accuracy of SI-DHM and to provide high-resolution phase imaging. In the training process, high-resolution amplitude and phase images obtained by phase-shifting SI-DHM together with wide-field amplitudes are used as inputs of DL-SI-DHM. The well-trained network can reconstruct both the high-resolution amplitude and phase images from a single wide-field amplitude image. Compared with the traditional SI-DHM, this method significantly shortens the recording time and simplifies the reconstruction process and complex phase correction, and frequency synthesizing are not required anymore. By comparsion, with other learning-based reconstruction schemes, the proposed network has better response to high frequencies. The possibility of using the proposed method for the investigation of different biological samples has been experimentally verified, and the low-noise characteristics were also proved.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 13; Pages 19247; 2021
DOI: 10.1364/oe.424718

Simplified digital content generation based on an inverse-directed propagation algorithm for holographic stereogram printing

Author(s):

Khuderchuluun, Anar; Piao, Yan-Ling; Erdenebat, Munkh-Uchral; Dashdavaa, Erkhembaatar; Lee, Moung Hee; Jeon, Seok-Hee & Kim, Nam

Abstract:

“Holographic stereogram (HS) printing requires extensive memory capacity and long computation time during perspective acquisition and implementation of the pixel re-arrangement algorithm. Hogels contain very weak depth information of the object. We propose a HS printing system that uses simplified digital content generation based on the inverse-directed propagation (IDP) algorithm for hogel generation. Specifically, the IDP algorithm generates an array of hogels using a simple process that acquires the full three-dimensional (3D) information of the object, including parallax, depth, color, and shading, via a computer-generated integral imaging technique. This technique requires a short computation time and is capable of accounting for occlusion and accommodation effects of the object points via the IDP algorithm. Parallel computing is utilized to produce a high-resolution hologram based on the properties of independent hogels. To demonstrate the proposed approach, optical experiments are conducted in which the natural 3D visualizations of real and virtual objects are printed on holographic material. Experimental results demonstrate the simplified computation involved in content generation using the proposed IDP-based HS printing system and the improved image quality of the holograms.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Volume 60; Number 14; Pages 4235; 2021
DOI: 10.1364/ao.423205

Twin curvilinear vortex beams

Author(s):

Wang, Zhuang; Yuan, Zheng; Gao, Yuan; Yan, Wenxiang; Liang, Chunjuan; Ren, Zhi-Cheng; Wang, Xi-Lin; Ding, Jianping & Wang, Hui-Tian

Abstract:

“We report on a novel curvilinear optical vortex beam named twin curvilinear vortex beams (TCVBs) with intensity and phase distribution along a pair of two- or three-dimensional curves, both of which share the same shape and the same topological charge. The TCVBs also possess the character of perfect optical vortex, namely having a size independent of topological charge. We theoretically demonstrate that a TCVB rather than a single-curve vortex beam can be created by the Fourier transform of a cylindrically polarized beam. The behavior of TCVBs generated through our method is investigated by simulation and experiment, including interference experiments for identifying the vortex property of the TCVBs. The TCVBs may find applications in optical tweezers, such as trapping low refractive index particles in the dark region between two curves and driving them moving along the curvilinear trajectory.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 9; Pages 14112; 2021
DOI: 10.1364/oe.423803
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